It has long been recognized that one of the most valuable products generated through the refining of crude mineral oils is lubricating oils. It is common practice to recover lubricating oil basestocks by solvent extracting, with a selective solvent, undesirable components such as sulfur compounds, oxygenated compounds, and aromatics from straight distillates. However, with the decline in the availability of paraffinic base crudes, and a corresponding increase in the proportion of naphthenic and asphaltic base crudes, it is becoming increasingly difficult to meet the demand for lubricating oil basestocks, or base oils.
Other conventional techniques for preparing basestocks include hydroconversion and solvent extraction. For example, U.S. Pat. No. 5,935,416, Cody et al., teaches a process wherein a lube oil boiling range feed is solvent extracted, stripped, and passed through two hydroconversion zones prior to hydrofinishing and then dewaxing, thus producing a lubricating oil basestock. Other processes such as U.S. Pat. No. 5,171,422, Kirker et al., and U.S. Pat. No. 6,217,747 B1, Chang et al., teach a process whereby a high quality lubricating oil basestock is produced by subjecting a high boiling range hydrocarbon stream to hydrocracking conditions. The U.S. Pat. No. 5,171,422 patent utilizes a high silica content zeolite catalyst of the faujasite type to produce a hydrocrackate product, and the U.S. Pat. No. 6,217,747 patent utilizes a hydrocracking catalyst comprising a hydrogenation/dehydrogenation component and an acidic solid component modified with an oxyanion to produce a hydrocrackate product. The hydrocrackate product is then processed to produce a lubricating oil basestock. One of the many drawbacks of lubricating oil refining utilizing hydroconversion, hydrocracking or solvent extraction is that such processes typically require severe operating conditions such as high pressure and temperature or high solvent:oil ratios and high extraction temperatures to produce high basestock qualities. Further, hydroconversion, hydrocracking or solvent extraction typically involve expensive operating conditions and low yields.
Further, even though hydroconversion, hydrocracking or solvent extraction can be used in lubricating oil refining, most lubricating oil feeds must also be dewaxed in order to produce lubricating oils which will remain fluid down to the lowest temperature of use. Dewaxing is the process of separating or converting hydrocarbons which solidify readily (i.e., waxes) in petroleum fractions. The catalytic dewaxing of wax and waxy feeds boiling in the lubricating oil range and catalysts useful in such processes are well known in the art. Generally these processes utilize catalysts comprising a molecular sieve component and a component selected from the Group VIII and/or Group VIB metals. Many examples of hydrodewaxing processes and catalysts commonly used are known in the art such as, for example, the processes and catalysts disclosed in U.S. Pat. No. 4,563,266, Hopkins et al., and U.S. Pat. No. 5,075,269, Degnan, et al.
It has also been proposed to solvent dewax a lube oil boiling range feed followed by catalytically dewaxing the solvent dewaxed lube oil stream. Examples of these processes can be found in U.S. Pat. No. 3,755,138, Chen et al., U.S. Pat. No. 4,622,130, Stephen C. Stem, and European Publication Number 0271265. However, processes such as those disclosed therein, and in similar processes, suffer from low yields, sometimes on the order of 50%, based on the lube oil feed. These processes also typically suffer from the catalytic dewaxing step altering key basestock properties such as viscosity and viscosity index.
While basestock quality is improving, further improvements in many properties, such as low temperature quality, as well as combinations of properties, such as superior low temperature fluidity at low product volatility, continue to challenge the industry. Benefits in low temperature performance would be beneficial for a wide range of formulated lubricants and would be particularly advantageous for passenger vehicle crankcase oils, automatic transmission fluids, automotive gear oils, hydraulic fluids, and commercial vehicle crankcase oils.
Low temperature quality for basestocks and base oils have historically been controlled using bulk property measurements such as pour point measured on the basestock, base oils, or formulated oil composition. However, small amounts of residual wax may not impact this bulk property measurement and, thus, small amounts of residual wax may go undetected through this simple analysis. This small amount of residual wax, however, does impact performance and can lead to issues such as crankcase oil gelling and loss of fluidity. Operating an engine in this scenario can lead to and has led to engine damage. Hence, the Mini-Rotary Viscometer (MRV) test was established to protect engines under cold weather conditions. The MRV test temperature is set by the Society of Automotive Engineers (SAE) J-300 Viscosity Classification system for each multigrade engine oil grade.
To improve the low temperature performance as measured by the MRV or other tests sensitive to very small amounts of residual wax, refineries utilizing solvent dewaxing can dewax to lower pour points. While this can be effective, improvements are still needed. Catalytic dewaxing, a relatively newer processing approach, is often more effective than solvent dewaxing, especially for the light and medium neutral stocks. However, many existing refineries in operation today utilize solvent dewaxing only and do not have the equipment available for catalytic dewaxing which often requires high quantities of pure hydrogen provided at high pressure and pre-treatment of feed to remove S and N.
Thus, as the demand for quality lube oil basestock continues to increase, the search for new and different processes, catalysts, and catalyst systems that exhibit improved activity, increased yields, selectivity and/or longevity is a continuous, ongoing exercise. Therefore, there is a need in the lube oil market to provide processes that can produce lube oil basestocks in ever-increasing yields that meet the demand for increased fuel economy, reduced emissions, etc.